The use of ultrasonic scalpel lowers the risk of post-mastectomy seroma formation in obese women.

: Seroma formation (SF) is the most common postoperative complication after mastectomy and axillary surgery. The aim of this study was to assess its incidence and risk factors following a modified radical mastectomy in breast cancer patients. : 271 patients who underwent a modified radical mastectomy (250 with traditional electrocautery and 21 with an ultrasonic scalpel) were studied. The SF rate was calculated and its association with patient-related factors, surgical features and postoperative variables was assessed and statistically analyzed with <0.05 as a significance threshold. : SF was observed in 18% of patients. Patient's age, operating time and number of removed axillary lymph nodes did not significantly differ between SF and non-SF patients. Patients BMI, total drainage amount, number of days with drain were higher and postoperative hospital stay was significantly longer in SF patients (<0.001 each). The dissection instrument was also an important risk factor: SF developed in 20% of patients operated with electrocautery and in none with an ultrasonic scalpel (<0.05). The association between surgical instrument and the number of removed lymph nodes, patient's age and BMI was not significant. Dissection with an ultrasonic scalpel resulted in a statistically significant lower total drainage amount. However, it was also related to a significantly longer operating time (<0.001 each). : Risk of SF after a modified radical mastectomy is significantly higher in patients with obesity. Despite longer operating time, using an ultrasonic scalpel is a valuable option in those cases because it lowers the total drainage amount and seems to be an important protective factor against SF.